In the related art, liquid developing agents and powder developing agents are used as the developing agent that makes visible images from electrostatic latent images but, when high quality images are required from electrostatic recording apparatus, a liquid developing agent is usually used. This is because the diameter of the toner particles in liquid developing agent is from 0.1 to 0.5 .mu.m, compared with toner particle diameters of 7 to 10 .mu.m in powder developing agents. Accordingly, the image resolution obtainable using liquid developing agents is higher than when a powder developing agent is used. In addition, powders generally flow less well than liquids. Thus, powder developing agents are more difficult to stir than liquid developing agents. Accordingly, uniform developing over wide areas is difficult to obtain if a powder developing agent is used.
Multi-color image formation apparatus in the related art is provided with one image bearing member and four developing agent bearing members, one each for the four developing agents, yellow, magenta, cyan, and black. The developing agent applied on each of the developing agent bearing members is supplied to the surface of the latent image on the image bearing member, thereby forming a developed image on the image bearing member. The developed image formed on the image bearing member is transferred to the substrate positioned on the charged transfer member which has an electric charge of opposite polarity to the toner. This type of image formation process performed for the yellow, magenta, cyan, and black developing agents in sequence results in formation of a color image on the substrate.
Image formation apparatus in the related art uses toner, that is, charged developing particles, to develop electrostatic latent images on an electrostatic latent image bearing member, then transfers the normal developed image that has been formed on the electrostatic latent image bearing member to the substrate. The method used to transfer the normal developed image that has been formed on an electrostatic latent image bearing member to the substrate is the method wherein a transfer member that has an electric charge of opposite polarity to the toner is made to contact the electrostatic latent image bearing member through the medium of the substrate such that electrostatic force is used to transfer the image to the substrate, thereby forming the image.
However, the multi-color image formation apparatus in the related art performs the above image formation processes sequentially for the yellow, magenta, cyan, and black developing agents in order to form color images. This makes it difficult to achieve high image printing speeds. In addition, the low-viscosity liquid developing agent usually used in the electrostatic recording and similar apparatus in the related art consists of IsoparG (registered trademark of the Exxon Corporation), an organic solvent, in which toner is mixed at a proportion of about 1 to 2% by weight. It is desirable to use a more highly concentrated liquid developing agent than that used in the apparatus of the related art and to reduce the volatility of the solvent to allow production of safer and simpler multi-color image formation apparatus, but this type of apparatus cannot be found in the related art. Moreover, the ideal method of forming multi-color images on a substrate when using a highly concentrated and highly viscous liquid developing agent (a liquid developing agent with a high viscosity of 100 to 10,000 mPa.cndot.s in which toner is dispersed at high concentrations in the non-conductive liquid) which adheres more strongly to the image bearing member was heretofore unknown.
The ideal method for transferring a developed image to the substrate to form an image without image inaccuracies occurring was heretofore unknown.
In addition, for the above apparatus in the related art, large quantities of liquid developing agent are required due to the low proportion of toner, and the IsoparG used as the non-conductive liquid (carrier liquid) is highly volatile and emits an unpleasant odour. Therefore, the apparatus in the related art causes an unpleasant work environment and environmental problems.